Congenital adrenal hyperplasia (CAH), resulting from mutations in CYP11B1, a gene encoding 11β-hydroxylase, represents a rare autosomal recessive Mendelian disorder of aberrant sex steroid production. Unlike CAH caused by 21-hydroxylase deficiency, the disease is far more common in the Middle East and North Africa, where consanguinity is common often resulting in identical mutations. Clinically, affected female newborns are profoundly virilized (Prader score of 4/5), and both genders display significantly advanced bone ages and are oftentimes hypertensive. We find that 11-deoxycortisol, not frequently measured, is the most robust biochemical marker for diagnosing 11β-hydroxylase deficiency. Finally, computational modeling of 25 missense mutations of CYP11B1 revealed that specific modifications in the heme-binding (R374W and R448C) or substrate-binding (W116C) site of 11β-hydroxylase, or alterations in its stability (L299P and G267S), may predict severe disease. Thus, we report clinical, genetic, hormonal, and structural effects of CYP11B1 gene mutations in the largest international cohort of 108 patients with steroid 11β-hydroxylase deficiency CAH.steroid hormones | missense mutations | classic CAH | ambiguous genitalia C ongenital adrenal hyperplasia (CAH) is a Mendelian disorder transmitted as an autosomal recessive trait. The most prevalent form of CAH arises from steroid 21-hydroxylase enzyme deficiency, accounting for ∼90-95% of all cases (1, 2). In contrast, CAH caused by steroid 11β-hydroxylase deficiency is considerably rare, with a prevalence of 5-8% (3), from which we estimate an overall frequency of 1 in 100,000 live births.Two homologous enzymes, 11β-hydroxylase and aldosterone synthase, are encoded by the CYP11B1 and CYP11B2 genes, respectively. The two genes are 40-kb apart, each comprising nine exons and mapped to chromosome 8q21-22 (3, 4) (Fig. 1A). In contrast to CYP21A2 and its CYP21A1P pseudogene, CYP11B1 and CYP11B2 are both active and do not have a pseudogene. The two encoded homologs, however, have distinct functions in cortisol and aldosterone synthesis, respectively (3). In the zona fasciculata, 11β-hydroxylase converts 11-deoxycortisol and 11-deoxycorticosterone to cortisol and corticosterone, respectively, and is regulated by adrenocorticotropic hormone secreted by the pituitary. In contrast, in the zona glomerulosa aldosterone synthase converts corticosterone to aldosterone with the intermediate production of 18-hydroxycorticosterone. These latter conversions are controlled mainly by the renin angiotensin II system and serum potassium concentration (3).Deficiency of 11β-hydroxylase prevents the conversion of 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone. This results in high levels of 11-deoxycortisol and 11-deoxycorticosterone, respectively, which are shunted into the androgen synthesis pathway, resulting in high levels of the androgenic steroid, androstenedione. Female newborns are thus profoundly virilized and exhibit significant masculinization of the ex...

Autosomal dominant hypophosphatemic rickets (ADHR) is a rare disease, characterized by isolated renal phosphate wasting, hypophosphatemia, and inappropriately normal 1,25-dihydroxyvitamin D(3) (calcitriol) levels. This syndrome involves rickets with bone deformities in childhood and osteomalacia, osteoporosis, articular and para-articular pain, and fatigue in adulthood. It is caused by mutations in a consensus sequence for proteolytic cleavage of the FGF23 protein. Normally, this protein actively regulates phosphate homeostasis. Here we report a Tunisian family in which one parent and three children show clinical and biological features of ADHR. Mutation analysis of the FGF23 gene finds a heterozygous substitution of the C at position 526 by a T (526 C --> T), leading to an amino acid replacement of the FGF23 protein (R176W) at position 176. This causative new mutation is located in the consensus sequence for the proteolytic cleavage domain. These results confirm the importance of this site in FGF23 function and its essential role in ADHR physiopathology.

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Purpose Macrozoospermia is a rare condition of male infertility characterized by the presence of close to 100 % largeheaded multiflagellar spermatozoa. The homozygous mutation (c.144delC) in aurora kinase C gene (AURKC) has been identified as the most frequent mutation causing macrozoospermia in North African patients. The aim of this study was to evaluate the prevalence of this condition in Tunisia and estimate the frequency of c.144delC mutation among infertile and control populations. Methods Sequencing c.144delC mutation was carried out in 33 macrozoospermic patients among 6652 infertile men. Minisequencing of exon3 was performed in 250 unrelated control individuals to estimate the frequency of c.144delC heterozygosity. Results More than 80 % of macrozoospermic patients were c.144delC homozygous. The prevalence of homozygous c.144delC was 0.4 % among infertile men (27/6652). The frequency of heterozygosity was 0.4 % among controls (1/250). Surprisingly, it is five times less common than established in the general population of North Africa (2 %) or in the Moroccan population (1.7 %).Conclusions We show that this mutation is relatively less frequent in the Tunisian population than in other Maghrebian populations. The occurrence of homozygous mutation among infertile men can be attributed to the high rate of consanguinity and its impact on the expression of this autosomal recessive male infertility disorder rather than a high frequency of heterozygous carriers among the general population. This highlights the importance of the molecular analysis of AURKC mutations for infertile men with high percentage of largeheaded multiflagellar spermatozoa in order to limit unnecessary in vitro fertilization attempts for them.